Indicator lamps are used for the optical signaling of a state of a device in which the indicator lamps are incorporated. For signaling that can be detected simply by an operator, the indicator lamps must have uniform and bright illumination from the front as far as a defined viewing angle, e.g. 60° with respect to a longitudinal axis of the indicator lamp.
For this purpose, indicator lamps are implemented, for example, with a diffuser, with which uniform illumination can be achieved over the (entire) surface of the indicator lamp. However, the provision of a diffuser, which is arranged between a light source and a transparent, frequently colored, covering, generally entails a loss of brightness. Omitting the diffuser certainly ensures a higher brightness but entails non-uniform illumination of the covering.
In order to permit a uniform brightness over the viewing area with, at the same time, a high luminous power, U.S. Pat. No. 4,758,701 proposes the use of two Fresnel lenses matched to each other between the light source and a covering. By way of the lens arrangement, the light emitted by the light source can emerge substantially in parallel from the covering.